In scuba diving, it is typical to use a diving suit, compressed-gas tanks and a breathing regulator connected to them, and a diving computer. The diving computer shows the diver information on the prevailing environment, such as depth, pressure, and diving time, and on the gases available, and on the basis of these calculates the parameters that are important to performance, with the aid of a decompression model programmed into the device. In terms of diving, an important parameter is the temporal sufficiency of the available gases and the safe ascent time in decompression diving.
When diving to a sufficient depth, or if diving lasts for a sufficient length of time, the diver's surfacing speed must be limited, when the term decompression diving is used. In deep diving, amounts of nitrogen, helium, and other inert gases, which depend on the partial pressure of the gas inhaled, collect in the diver's blood circulation and tissues. The accumulated nitrogen causes problems when the diver rises towards the surface, when the ambient pressure decreases, leading to an increased risk of decompression sickness. The partial pressure of precisely nitrogen and helium is therefore monitored carefully when diving. Decompression sickness is a state in which nitrogen that has expanded in the blood or tissue due to a reduction in pressure forms bubbles, which, when they expand, can block blood vessels and damage tissue. To reduce the risk, the diver must observe at least one compulsory safety stop during ascent. The diving computer typically determines the depth for performing the safety stop or stops and the decompression time, by calculating them on the basis of the diving profile and decompression model, as well as of the prevailing conditions.
Commercial diving computers are previously known, which calculate a suitable decompression time based on the programmed gases. For example, VR Technology Ltd.'s VR3 diving computer prepares a dive plan based on the programmed gases, in such a way that the device calculates the time required for ascent by adapting the available gases to the prevailing conditions. The VR3 diving computer receives the data entered by the diver prior to diving. All the available gases, of which there can be ten, are entered in the device. Based on the content of these gases and on the depth, the computer calculates the necessary ascent time. In the calculation, the device seeks to optimize performance so that the gases fed to the diver are used at their optimal depth. However, the device's calculation algorithm allows for the effects of the duration of the necessary safety stops, and a possible failure to observe them, for instance on flying after diving.
The Suunto Vytec diving computer is also known, into which the diver can programme the available diving gases, prior to diving. During diving, the device's calculation algorithm suggests safety stops to avoid decompression sickness. The Vytec diving computer's algorithm on the other hand is based on calculating the necessary ascent time on the assumption that, during the ascent, the diver will not use other gases than the gas selected at each time. If the diver changes the selected gas and selects another gas programmed in the computer, the diving computer calculates the necessary ascent time by assuming that the selected gas will be used to ascend to the surface. In addition, only the diving gases carried by the diver are configured into the Vytec device.
In addition, a diving-gas mixing system is known from publication U.S. Pat. No. 5,794,616, which automatically uses the gas data for the gas in each of three tanks.
However, significant drawbacks are associated with the prior art. This is because, in diving computers according to the prior art, gases cannot be configured as primary and secondary gases, so that in problem situations during diving the diver may have very little time to react to the situation, because he must alter the mixture while subject to the stress arising from the problem. In known solutions, the gases of a diving partner or deco-station cannot be programmed as reserve, i.e. secondary gases, in case of possible problem situations. Thus, they cannot be exploited computationally in decompression, without them interfering with the calculation of the optimal dive plan and without the diving computer permitting their use, if their maximum operating depth permits. On the other hand, even reserve gases being carried cannot be programmed as described above, so that the dive cannot be optimized with the aid of the available decompression gases, in such a way that the dive plan's optimized length of time on the bottom would be altered for a possible safer surfacing.
The present invention is intended to resolve at least some of the problems of the prior art and to create an improved method for determining ascent time in a diving computer, as well as a diving computer and a computer program.